As .COM is the natural domain extension for the United States based websites, it does get some priority in the Google.com’s search engine results (based on Google’s US datacenters) when competing against other countries’ domain extensions like .CO.UK, .CO.ZA, .COM.AU etc. However, .COMs don’t get automatic priority over other similar extensions like .ORG, .NET etc. that are also commonly used in the United States. All these domain extensions compete with .COMs on a level playing field.
In theory, you could technically acquire a domain for $10,000 and be able to sell it for $100,000. You could also acquire a domain for $10 and be able to sell it for $100,000, $10,000… or $100, you get the picture. Because of this, it’s hard to recommend a perfect starting budget because your strategy, experience, and the pace at which you learn will hugely affect your buying and selling decisions.